9-bit to10-bit encoder and decoder

ABSTRACT

The field of the invention is that of serial digital data transmissions. Such digital data is, in particular, of video type. In certain types of transmission, the links used cannot pass direct current. Such is the case in particular with the so-called “AC-coupled” links used in aeronautics for transferring video signals between computers. In this case, it becomes essential to transmit binary words comprising, if possible, similar quantities of zeroes and ones. The subject of the invention is an encoder or a decoder of 9-bit binary words into 10-bit binary words, said 10-bit binary words being designed to be transmitted over links that cannot pass direct current, said binary words comprising between four ones and six ones regardless of the initial 9-bit binary word.

RELATED APPLICATIONS

The present Application is based on International Application No.PCT/EP2005/053965, filed Aug. 11, 2005, which in turn corresponds toFrench Application No. 04/08881 filed on Aug. 13, 2004 and priority ishereby claimed under 35 USC §119 based on these applications. Each ofthese applications are hereby incorporated by reference in theirentirety into the present application.

FIELD OF THE INVENTION

The field of the invention is that of serial digital data transmissions.Such digital data is, in particular, of video type.

DESCRIPTION OF THE PRIOR ART

There are currently families of digital components very well suited tothe serial transmission of digital data consisting of words encoded on10 bits. These components are manufactured by NATIONAL SEMICONDUCTOR,MAXIM and TEXAS. These components are normally inexpensive, small andconsume little. Transmission is more often than not handled by addingtwo complementary bits to each 10-bit word, the first being a one andthe second being a zero. The addition of the two bits slightly increasesthe bandwidth needed for transmission but presents certain advantages.These include, in particular:

-   -   Limiting the maximum length of the word without transitions, the        two additional bits being complementary and so generating a        systematic transition.    -   The recovery of the boundaries of the word in the serial data        stream by controlling the permanent repetitiveness of the        transition given by the two complementary bits.

The bearer for this serial transmission can be either an electric cableor an optical fiber.

Apart from the synchronization condition of the link, the content of the10 bits of each word is left free to be chosen by the user, the digitalcomponents dedicated to transmission not comprising any dataencoding/decoding device. Consequently, the number of zeroes or ones ineach word is not controlled and can vary between 0 and 10. The signalcan therefore comprise words with a large number of successive ones orzeroes. This does not pose any problems when the link transmits directcurrent. As an example, there are short links in a favorable environmentor “backplane” type links located inside electronic units whichinterlink the various electronic cards.

However, in certain types of transmission, the links used cannot passdirect current. Such is the case in particular with the so-called“AC-coupled” links used in aeronautics for transferring video signalsbetween computers. In this case, if the digital word transmitted has alarge number of successive ones or zeroes, the transmission can becorrupted. Consequently, it becomes essential to transmit binary wordscomprising, if possible, similar quantities of zeroes and ones. Morespecifically, for a 10-bit word, it is important for the number of onesor zeroes to be between 4 and 6.

To solve this problem, there are currently various types of encoding.

A first solution consists in using a block encoding system. The standardencoding systems are either so-called “4B-5B” or “8B-10B” encodingsystems. Thus, 4-bit words are converted into 5-bit words and 8-bitwords are converted into 10-bit words. The drawback with these codes isthat the number of useful bits in a word encoded on 10 bits is reducedto 8. Thus, transmitting a standard video signal comprising threeprimary signals consisting of 6-bit words, or a transmission of 18 bitsin total, entails using three serial links each transmitting 10-bitwords whereas, in principle, two links each transmitting 10-bit wordswould be sufficient, so making it possible to significantly reduce thenumber of cables, the complexity and the cost of the electronics neededfor the transmission.

A second solution consists in scrambling the data word in apseudo-random manner. This function is called “scrambler”. For example,the “10B-10B” encoding system defined by the SMPTE 259 video standard(SMPTE standing for Society of Motion Picture and Television Engineers)can be used. This solution has the advantage of not wasting bits.However, this solution does have the drawback that certain sequences ofwords generate “pathological patterns” which block the scrambling andwhich can lead to transient cases where the words have an average valuein terms of quantities of ones or zeroes incompatible with the bandwidthof the coupling transformers.

SUMMARY OF THE INVENTION

The inventive system of encoding and decoding makes it possible toresolve the above drawbacks at the price of an increase in the minimumnumber of bits. In practice, the device described is a “9B-10B” typeencoder which can be used to encode an initial signal consisting of9-bit words into a signal consisting of 10-bit words so as to be able totransmit it uncorrupted by means of links that do not pass directcurrent. Naturally, the associated “9B-10B” decoder can be used toperform the reverse function. It decodes a received signal consisting of10-bit words into a signal consisting of 9-bit words making it possibleto retrieve the original signal.

Thus, it is possible to encode or decode a video signal consisting ofthree signals of 6-bit words into two signals of 10-bit words, reducingthe number of links needed to transmit the video signal to two.

More specifically, the subject of the invention is an encoder of a 9-bitbinary word into a 10-bit binary word, said encoder comprising encodingmeans, characterized in that said means perform at least the followingencoding operations:

-   -   The encoding of a 9-bit binary word comprising three ones or        four ones is obtained by adding a one to said 9-bit word to        obtain an encoded 10-bit word;    -   The encoding of a 9-bit binary word comprising five ones or six        ones is obtained by adding a zero to said 9-bit word to obtain        an encoded 10-bit word.

Advantageously, the encoding means perform the following encodingoperations:

-   -   The encoding of a 9-bit binary word comprising fewer than three        ones is a 10-bit binary word comprising four ones and beginning        with a zero.    -   The encoding of a 9-bit binary word comprising more than six        ones is a 10-bit binary word comprising six ones and beginning        with a one.

Advantageously, the encoded form of a 9-bit binary word comprising twoones is a 10-bit binary word comprising four ones, beginning with azero, the nine remaining bits being generated from the original 9-bitword, by replacing two adjacent zeroes in said word with two ones suchthat the 36 possible 9-bit words comprising two ones all have adifferentiated encoding.

Also, the encoded form of a 9-bit binary word comprising a one is a10-bit binary word comprising four ones, beginning with a zero andcomprising a sequence of 4 bits made up of four successive ones, saidsequence possibly being in two parts, a first part located at the end ofthe 10-bit word and the second part located at the start of the 10-bitword after the first zero, such that the nine possible 9-bit wordsincluding a one all have a differentiated encoding.

Advantageously, the encoded form of a 9-bit binary word comprising twozeroes is a 10-bit binary word comprising four zeroes, beginning with aone, the nine remaining bits being generated from the original 9-bitword, by replacing two adjacent ones in said word with two zeroes suchthat the 36 possible 9-bit words comprising two zeroes all have adifferentiated encoding.

Advantageously, the encoded form of a 9-bit binary word comprising a oneis a 10-bit binary word comprising four zeroes, beginning with a one andcomprising a sequence of 4 bits made up of four successive zeroes, saidsequence possibly being in two parts, a first part located at the end ofthe 10-bit word and the second part located at the start of the 10-bitword after the first one, such that the nine possible 9-bit wordsincluding a zero all have a differentiated encoding.

The invention also relates to a decoder of a 10-bit binary word into a9-bit binary word, said decoder comprising decoding means, characterizedin that said means perform decoding operations only on 10-bit wordscomprising four ones or five ones or six ones.

Advantageously, the decoding means perform at least the followingdecoding operations:

-   -   The decoding of a 10-bit binary word comprising five ones is        obtained by deleting the first bit from said 10-bit word to        obtain a decoded 9-bit word;    -   The decoding of a 10-bit binary word comprising four ones and        the first bit of which is a one is obtained by deleting the        first bit from said 10-bit word to obtain a decoded 9-bit word;    -   The decoding of a 10-bit binary word comprising six ones and the        first bit of which is a zero is obtained by deleting the first        bit from said 10-bit word to obtain a decoded 9-bit word.

Advantageously, the decoding means perform the following decodingoperations:

-   -   The decoding of a 10-bit binary word comprising four ones and        the first bit of which is a zero is obtained by deleting the        first bit and by changing at least two ones into zeroes to        obtain a 9-bit word comprising no more than two ones.

Also, the decoding means perform the following decoding operations:

-   -   The decoding of a 10-bit binary word comprising six ones and the        first bit of which is a one is obtained by deleting the first        bit and by changing at least two zeroes into ones to obtain a        9-bit word comprising at least seven ones.

Advantageously, an encoder or a decoder according to the invention isincorporated in a programmable digital component, in particular of theFPGA (Fast Programmable Gate Array) type or of the ASIC(Application-Specific Integrated Circuit) type for applications with thetransmission or reception of a digital video signal consisting of 10-bitwords.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other advantages will becomeapparent from reading the description that follows given by way ofnonlimiting example and from the appended figures, among which:

FIG. 1 represents tables showing the distribution of the number of onesin the 9-bit and 10-bit words;

FIG. 2 represents the encoding/decoding mapping according to theinvention between the 9-bit words and the associated 10-bit words;

FIGS. 3 to 11 represent, for an exemplary 9-bit word containing a numberof ones varying from 0 to 9, the encoding in the associated 10-bit word;

FIGS. 12 and 13 represent two tables comprising eight pairs of columns,each pair of columns giving in hexadecimal the encoding and the decodingof a 9-bit word into a 10-bit word for the 9-bit words between 000 and 1FF;

FIGS. 14 and 15 represent theoretical circuit diagrams of the encoderand the decoder according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

There are 2⁹ different 9-bit words, or 512 in all, and there are 2¹⁰different 10-bit words, or 1024 in all. The tables in FIG. 1 representthe distribution of the quantity Q of ones in the 9-bit and 10-bitwords. As has already been stated, it is essential, to secure the link,for the 10-bit words to comprise a balanced number of ones and zeroes.Now, the second table in FIG. 1 shows that there are a total of 67210-bit words that have between four and six ones. There are thereforeenough 10-bit words that have this property to encode the 512 9-bitwords.

To best simplify the encoding and decoding means, it is imperative touse encoding and decoding rules that least modify the initial 9-bit or10-bit words.

FIG. 2 represents a mapping table between the 512 9-bit words and 512associated 10-bit words, the first bit of a 10-bit word being denotedD9. By examining the table, it can be seen that:

-   -   There are as many 9-bit words comprising three ones as 10-bit        words comprising four ones and beginning with a one;    -   There are as many 9-bit words comprising four ones as there are        10-bit words comprising five ones and beginning with a one;    -   There are as many 9-bit words comprising five ones as there are        10-bit words comprising five ones and beginning with a zero;    -   There are as many 9-bit words comprising six ones as there are        10-bit words comprising six ones and beginning with a zero.

Based on these observations, the encoding of the 9-bit words comprising3, 4, 5 or 6 ones into 10-bit words is simple and obeys the followingrules:

-   -   The encoding of a 9-bit binary word comprising three ones or        four ones is obtained by adding a one to said 9-bit word to        obtain an encoded 10-bit word;    -   The encoding of a 9-bit binary word comprising five ones or six        ones is obtained by adding a zero to said 9-bit word to obtain        an encoded 10-bit word.

Naturally, the rules for decoding 10-bit words

-   -   comprising four ones and beginning with a one;    -   or comprising five ones;    -   or comprising six ones and beginning with a zero can immediately        be deduced:    -   The decoding of a 10-bit binary word comprising five ones is        obtained by deleting the first bit from said 10-bit word to        obtain a decoded 9-bit word;    -   The decoding of a 10-bit binary word comprising four ones and        the first bit of which is a one is obtained by deleting the        first bit from said 10-bit word to obtain a decoded 9-bit word;    -   The decoding of a 10-bit binary word comprising six ones and the        first bit of which is a zero is obtained by deleting the first        bit from said 10-bit word to obtain a decoded 9-bit word.

These simple rules can be used to encode 420 9-bit words.

There are still 92 9-bit words comprising either fewer than three onesor more than six ones to be encoded.

As an example, the encoding and decoding rules according to theinvention are detailed below:

-   -   The encoded form of a 9-bit binary word comprising two ones is a        10-bit binary word comprising four ones, beginning with a zero,        the nine remaining bits being generated from the original 9-bit        word, by replacing two adjacent zeroes of said word with two        ones, such that the 36 possible 9-bit words with two ones all        have a differentiated encoding.    -   The encoded form of a 9-bit binary word comprising a one is a        10-bit binary word comprising four ones, beginning with a zero        and comprising a sequence of four bits made up of four        successive ones, said sequence possibly being in two parts, a        first part located at the end of the 10-bit word and the second        part located at the start of the 10-bit word after the first        zero.    -   The encoded form of a 9-bit binary word comprising two zeroes or        seven ones is a 10-bit binary word comprising four zeroes,        beginning with an added one, the remaining 9 bits being        generated from the original 9-bit word, by replacing two        adjacent ones with zeroes, such that the 36 possible words all        have a differentiated encoding.    -   The encoded form of a 9-bit binary word comprising one zero or        eight ones is a 10-bit binary word comprising four zeroes,        beginning with an added one and comprising a sequence of four        bits made up of four successive zeroes, said sequence possibly        being in two parts, a first part located at the end of the        10-bit word and the second part located at the start of the        10-bit word after the first added one such that the nine        possible 9-bit words with a zero all have a differentiated        encoding.    -   The decoding of a 10-bit binary word comprising four ones and        the first bit of which is a zero is obtained by deleting the        first bit and by changing at least two ones into zeroes to        obtain a 9-bit word with no more than two ones.    -   The decoding of a 10-bit binary word comprising six ones and the        first bit of which is a one is obtained by deleting the first        bit and by changing at least two zeroes into ones to obtain a        9-bit word with at least seven ones.

FIG. 3 to 11 represent, for a 9-bit word comprising an increasing numberof ones ranging from 0 to 9, the encoding of the corresponding 10-bitword according to the encoding rules stated above.

FIGS. 12 and 13 represent two tables with eight pairs of columns, eachpair of columns giving in hexadecimal the encoding and the decodingaccording to the invention of a 9-bit word into a 10-bit word for the9-bit words between 000 and 1 FF, or in decimal, all the 9-bit wordsbetween 0 and 511.

As has been seen, even by retaining only the 10-bit words comprisingfour to six ones, there still remain 160 10-bit words with four or sixones for which there is no corresponding 9-bit word. These words can beused, for example, to encode synchronization information or auxiliarywords.

As a nonlimiting example, the encoder or the decoder according to theinvention is implemented in a programmable digital component, inparticular of FPGA (Fast Programmable Gate Array) type or of ASIC(Application-Specific Integrated Circuit) type.

The words can be encoded either in the form of a programmed logicobserving the inventive encoding rules, or in the form of an encodingtable equivalent to the tables of FIGS. 12 and 13, or in a hybrid form,combining programmed logic and encoding table.

FIGS. 14 and 15 illustrate, as a nonlimiting example, exemplaryimplementations of encoder and decoder in a programmable digitalcomponent 10 represented by a dotted line rectangle in said figures.These devices are used to handle video signal transmission.

The device illustrated in FIG. 14 is used to encode the signaltransmitted before transmission via a link not represented in thefigure. The original video signal 100 represented by a bold line arrowis made up of 9-bit words. The encoder 1 encodes said words into 10-bitwords according to the inventive encoding procedures. The encoder thusdelivers a first signal 101 consisting of 10-bit words. Dedicatedelectronic functions of the programmable digital component symbolized bythe rectangle 3 in FIG. 14 generate synchronization sequences of SAV(Start of Active Video) type and of EAV (End of Active Video) type,which can be identical or similar to those defined by the standardCCIR-601. Preferably, these sequences can be made up of 10-bit wordscomprising four ones or six ones, words not used for the encoding of the9-bit words. However, it is also possible to use standard wordscorresponding to the video standards such as the hexadecimal words 000or 3FF, given that, since these sequences are short, they do notsignificantly degrade the average value of the quantities of ones andzeroes transmitted. These synchronization sequences are inserted atinstants when the video signal contains no video information of use tothe multiplexing means 2 which thus supplies a signal 102 comprisingboth the 10-bit encoded words corresponding to the video signal 100 andthe synchronization signals.

The transmit circuits also take account of the so-called “byte”synchronization constraint of the deserializer of the transmissioncomponent. This constraint entails sending, for a sufficiently longtime, the word 01 F corresponding to five zeroes followed by fivesuccessive ones at least 1024 times in succession. Thus, thesynchronization can be achieved without ambiguity. This transmission canbe performed during the vertical blanking phase of the video signal,sometimes also called “vertical back porch”.

The device illustrated in FIG. 15 is used to decode the signal receivedafter transmission via a link not represented in the figure. Theoriginal video signal 102 represented by a bold line arrow is made up of10-bit words. The signal received is sent to the decoder 4 and to asynchronization decoder 5 that is used to synchronize the video signal,this synchronization being symbolized by a thick vertical arrow linkingitems 4 and 5. The decoder 4 transmits two signals:

-   -   the decoded signal 100 proper consisting of 9-bit words        symbolized by a thick arrow;    -   an error signal 103 when the encoded 10-bit word does not        correspond to any 9-bit word.

1. An encoder of a 9-bit binary word into a 10-bit binary word, saidencoder comprising: encoding means, for: encoding of a 9-bit binary wordhaving three ones or four ones by adding a one to said 9-bit word toobtain an encoded 10-bit word, encoding of a 9-bit binary word havingfive ones or six ones by adding a zero to said 9-bit word to obtain anencoded 10-bit word, encoding of a 9-bit binary word having fewer thanthree ones to obtain a 10-bit binary word having four ones and beginningwith a zero, and for encoding of a 9-bit binary word having more thansix to obtain into a 10-bit binary word having six ones and beginningwith a one.
 2. The encoder as claimed in claim 1, wherein the encodedform of a 9-bit binary word having two ones is a 10-bit binary wordhaving four ones, beginning with an added zero, the nine remaining bitsbeing generated from the original 9-bit word, by replacing two adjacentzeroes with ones such that the 36 possible 9-bit words having two onesare all differentiated.
 3. The encoder as claimed in claim 1, whereinthe encoded form of a 9-bit binary word having a one is a 10-bit binaryword having four ones, beginning with an added zero and having asequence of 4 bits made up of four successive ones, said sequencepossibly being in two parts, a first part located at the end of the10-bit word and the second part located at the start of the 10-bit wordafter the first added zero.
 4. The encoder as claimed in claim 1,wherein the encoded form of a 9-bit binary word having two zeroes is a10-bit binary word having four zeroes, beginning with an added one, the9 bits being generated from the original 9-bit word, by replacing twoadjacent ones with zeroes such that the 36 possible 9-bit words are alldifferentiated.
 5. The encoder as claimed in claim 1, wherein theencoded form of a 9-bit binary word having a zero is a 10-bit binaryword having four zeroes, beginning with an added one and comprising asequence of 4 bits made up of four successive zeroes, said sequencepossibly being in two parts, a first part located at the end of the10-bit word and the second part located at the start of the 10-bit wordafter the first added one.
 6. A decoder of a 10-bit binary word encodedby an encoder as claimed in claim 1 into a 9-bit binary word, saiddecoder having decoding means, wherein said means perform decodingoperations only on 10-bit words having four ones or five ones or sixones and wherein the decoding means performs at least the followingdecoding operations: decoding of a 10-bit binary word having five onesby deleting the first bit from said 10-bit word to obtain a decoded9-bit word; decoding of a 10-bit binary word having four ones and thefirst bit of which is a one by deleting the first bit from said 10-bitword to obtain a decoded 9-bit word; and decoding of a 10-bit binaryword having six ones and the first bit of which is a zero by deletingthe first bit from said 10-bit word to obtain a decoded 9-bit word. 7.The decoder as claimed in claim 6, wherein the decoding means performthe following decoding operations: decoding of a 10-bit binary wordhaving four ones and the first bit of which is a zero is obtained bydeleting the first bit and by changing at least two ones into zeroes toobtain a 9-bit word having no more than two ones.
 8. The decoder asclaimed in claim 6, wherein the decoding means perform the followingdecoding operations: decoding of a 10-bit binary word having six onesand the first bit of which is a one is obtained by deleting the firstbit and by changing at least two zeroes into ones to obtain a 9-bit wordhaving seven ones.
 9. An encoding method for encoding a 9-bit binaryword into a 10-bit binary word, comprising the steps of: encoding of a9-bit binary word having three ones or four ones by adding a one to said9-bit word to obtain an encoded 10-bit word, encoding of a 9-bit binaryword having five ones or six ones obtained by adding a zero to said9-bit word to obtain an encoded 10-bit word, encoding of a 9-bit binaryword having fewer than three ones to obtain a 10-bit binary word havingfour ones and beginning with a zero; and encoding of a 9-bit binary wordhaving more than six ones to obtain a 10-bit binary word comprising sixones and beginning with a one.